Asio and Boost.Asio

Asio comes in two variants: (non-Boost) Asio and Boost.Asio. The
differences between the two are outlined below.

What are the differences in the source code?

— Asio is in a namespace called asio::, whereas Boost.Asio puts
everything under boost::asio::.

— The main Asio header file is called asio.hpp. The corresponding
header in Boost.Asio is boost/asio.hpp. All other headers are
similarly changed.

— Any macros used by or defined in Asio are prefixed with ASIO_. In
Boost.Asio they are prefixed with BOOST_ASIO_.

— Asio includes a class for launching threads: asio::thread.
Boost.Asio does not include this class, to avoid overlap with the
Boost.Thread library

— Boost.Asio uses the Boost.System library to provide support for error
codes ( boost::system::error_code and boost::system::system_error).
Asio includes these under its own namespace ( asio::error_code and
asio::system_error). For C++11, Asio uses the std::error_code and
std::system_error classes shipped with the compiler. When not using
C++11, the Boost.System version of these classes currently supports
better extensibility for user-defined error codes.

— Asio is header-file-only and for most uses does not require linking
against any Boost library. When using C++11 with recent versions of
gcc, clang or MSVC, Asio can be used independently of Boost by
defining ASIO_STANDALONE when you compile. Boost.Asio always requires
that you link against the Boost.System library, and also against
Boost.Thread if you want to launch threads using boost::thread.

Where do I get a release package?

Asio is available for download from SourceForge, in a package named
asio-X.Y.Z.tar.gz (or .tar.bz2 or .zip).

Boost.Asio is included in the Boost distributions for version 1.35 and
later. It is also available as a separate package on SourceForge, named
boost_asio_X_Y_Z.tar.gz. The latter is intended to be copied over the
top of an existing Boost source code distribution.

Where are the source code repositories?

How are both versions maintained?

All development is done in the Asio repository on
GitHub. The source is
periodically converted into Boost format using a script called
boostify.pl, and the changes merged into the Boost GitHub
repository.

Will Asio be discontinued now that Boost.Asio is included with Boost?

No. There are projects using Asio and they will continue to be
supported.

Should I use Asio or Boost.Asio?

It depends. Here are some things to consider:

— If you prefer the convenience of header-file-only libraries then using
Asio over Boost.Asio is suggested.

— If you must use a version of Boost older than 1.35 then Boost.Asio is
not included. You can use Boost.Asio by copying it over the top of your
Boost distribution (see above), but not everyone is comfortable doing
this. In that case, using Asio over Boost.Asio is suggested.

— New versions of both the Asio and Boost.Asio packages will be created
on a faster release cycle than that followed by Boost. If you want to
use the latest features you can still use Boost.Asio as long as you are
happy to copy it over the top of your Boost distribution. If you don’t
want to do this, use Asio rather than Boost.Asio.

Can Asio and Boost.Asio coexist in the same program?

Yes. Since they use different namespaces there should be no conflicts,
although obviously the types themselves are not interchangeable. (In
case you’re wondering why you might want to do this, consider a
situation where a program is using third party libraries that are also
using Asio internally.)